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uniquorn

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Re: "Stupid" Questions :o
« Reply #2700 on: October 22, 2019, 11:10:42 PM »
the increased density of surface waters as they cool and sink create enough convection to stir up the top tens of meters of ocean, getting all that heat to the surface.
Are you sure about that? itp103 microcats at 5m and 6m in the Beaufort recently, temperatures only occasionally peaking at the entrance to the amundsen gulf.

slow wing

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Re: "Stupid" Questions :o
« Reply #2701 on: October 23, 2019, 06:24:33 AM »
Thanks for all your interesting & some authoritative responses in this discussion.




I still don't understand, how can you use a very thin slice of a full model to approximate the true situation?

I can do it because a) I am only seeking order-of-magnitude accuracy & b) am considering the limited & somewhat artificial situation where the only heat transport mechanism is thermal conduction.



I think I found a better approximation in this article: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6114986/

This is comparing apples to oranges. You're showing an amount of heat whereas I calculated a rate of heat transfer. That's a lot of heat but it still has to get to the surface to affect the ice.




Have you all forgot the basics of sea ice formation? RoxTheGeologids, macid, slow wing?

Yes, I'm worried that some of the people here may have forgotten more about that than you or I ever knew.




I hope that the current expedition will show how this happens in real time! It's a really interesting theory.. lets see if the real world works that way.

Yes, an exciting prospect!
« Last Edit: October 23, 2019, 06:52:39 AM by slow wing »

binntho

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Re: "Stupid" Questions :o
« Reply #2702 on: October 24, 2019, 08:01:50 AM »
the increased density of surface waters as they cool and sink create enough convection to stir up the top tens of meters of ocean, getting all that heat to the surface.
Are you sure about that? itp103 microcats at 5m and 6m in the Beaufort recently, temperatures only occasionally peaking at the entrance to the amundsen gulf.

No, I'm not at all sure that it will stir up the top tens of meters. When I wrote that a couple of days ago, I had just been reading on Wikipedia that the top 100-150 meters were involved, and didn't really believe that it could be that much (or, as is more likely, that I had totally misunderstood what they were saying). So I tempered it down to "tens of meters".

But the point perhaps is that the accumulated SSTs in these seas is significant, and given that heat absorbtion is by far greatest in the top layers, perhaps the heat doesn't go all that deep. And when atmospheric temperatures start to go down below the SST then the process of cooling and sinking kicks in, resulting in a fairly efficient heat transfer to the surface.

Perhaps the best evidence for the efficiency of this heat transfer is the (admittedly anectdotal, but seemingly robust) tendency for the ocean surface not to start freezing until the air temps hit around -11C.

Since the freezing point of the surface is -1.8C, the -11C doesn't make sense unless you see it as breaching the cooling-induced turbulence, and managing to actually freeze the top layer before it sinks. Which again tells you that this turulence is strong enough to keep the ocean ice free in the current temps of between -2 and -3 in most of the still non-frozen parts of the Beaufort, Chukchi, Laptev and EES.

Of course there is a balance ongoing here. The winds off the centra Siberian coast, and off the ice  itself, are around or below -10C, but the warm up very quickly as they flow in over the high SST sea surface, with turbulence bringing cold air downwards as the bottom layers warm up, and at the same time sending the top ocean layer downwards as it cools.

Bottom line: Storminess is not needed to retard the onset of freezing in high SST situations. And higher SSTs does not indicate that more heat gets trapped beneath the ice.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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Aporia_filia

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Re: "Stupid" Questions :o
« Reply #2703 on: October 24, 2019, 12:13:30 PM »
Provably this is a real stupid question, but can not find a simple explanation of what should(?) be the main physical effect of warming the atmosphere: thermal expansion.
It is always treated when talking about seas.
There are a few papers on 'regional' effects like this https://www.atmos-chem-phys.net/18/15975/2018/
But, how could we spect the atmosphere respond to it, increasing its whole size, only part of it's layers, not the size but total pressure, what happens to the exchange with outer space???

kassy

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Re: "Stupid" Questions :o
« Reply #2704 on: October 24, 2019, 01:59:50 PM »
There are some different effects for the different atmospheric layers. I think you will find more if you look for the effect on specific layers like f.e. the troposphere.

random upper atmosphere example to show why it might be better to look for specific layer + effect of climate change instead of thermal expansion:
http://www.realclimate.org/index.php/archives/2006/11/the-sky-is-falling/

ETA:
https://phys.org/news/2006-12-climate-affecting-earth-outermost-atmosphere.html

Another example and fine links below too.
« Last Edit: October 24, 2019, 04:33:01 PM by kassy »
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binntho

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Re: "Stupid" Questions :o
« Reply #2705 on: October 24, 2019, 02:36:16 PM »
The stratosphere is cooling down as the troposphere warms up, apparently one of the tell-tale signs of greenhous-induced global warming, so perhaps the total atmospheric volume is not changing all that much due to warming?

https://skepticalscience.com/Stratospheric_Cooling.html

The Hadley cell is apparently expanding, see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4378390/

Changes in cloud height could be a symptom of troposphere expansion - apparently cloud height drops in La Nina years rises in El Nino years, but is it trending upwards? Some research says no, a paper from 2012 seems to be saying that the cloud base is dropping, but then I re-found this paper from 2016 that finds that clouds are moving upwards and polewards due to global warming: https://www.nature.com/articles/nature18273
because a thing is eloquently expressed it should not be taken to be as necessarily true
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Alumril

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Re: "Stupid" Questions :o
« Reply #2706 on: October 24, 2019, 03:34:08 PM »
I'm looking for recent methane concentration data from the Tiksi weather station, but the most recent data I can find on the NOAA website is over a year old.

Is the station still operational? Is NOAA still collecting this data? Or am I just being impatient?
« Last Edit: October 24, 2019, 11:39:43 PM by Alumril »

Aporia_filia

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Re: "Stupid" Questions :o
« Reply #2707 on: October 24, 2019, 08:22:07 PM »
Thanks a lot, you two.

RoxTheGeologist

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Re: "Stupid" Questions :o
« Reply #2708 on: October 24, 2019, 10:00:19 PM »
Have you all forgot the basics of sea ice formation? RoxTheGeologids, macid, slow wing?

Sea ice is densest at freezing point, and thus does not freeze in the same way that lake ice does. So slow wings "model" is patently wrong, and the increased density of surface waters as they cool and sink create enough convection to stir up the top tens of meters of ocean, getting all that heat to the surface.

Which is not to say that wave action will also create turbulence.

The current ice-free areas have a fair amount of wind according to NullSchool, but more importantly, the air temps are nowhere near low enough to start freezing.

I think that's what I said. I don't understand where I went wrong with my statement. Please edify!

binntho

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Re: "Stupid" Questions :o
« Reply #2709 on: October 25, 2019, 07:45:40 AM »
Have you all forgot the basics of sea ice formation? RoxTheGeologids, macid, slow wing?

Sea ice is densest at freezing point, and thus does not freeze in the same way that lake ice does. So slow wings "model" is patently wrong, and the increased density of surface waters as they cool and sink create enough convection to stir up the top tens of meters of ocean, getting all that heat to the surface.

Which is not to say that wave action will also create turbulence.

The current ice-free areas have a fair amount of wind according to NullSchool, but more importantly, the air temps are nowhere near low enough to start freezing.

I think that's what I said. I don't understand where I went wrong with my statement. Please edify!

Well, that's not what I read. In this comment,

As ice forms the ice is fresher than the seawater, the salts partitioning into the water. The denser cold, salty water sinks, creating convection. This causes the upper mixed layer to, well, mix, and deepen.  My guess is that it slows down the ice formation, but the mechanism needs ice to be growing before heat starts to move up from deeper layers.

you talk about the formation of ice as causing the sinking of the upper layers, and you claim that ice not only needs to form but needs to be growing before heat starts to move up.

So you are claiming a mechanism for heat transfer to the surface that is based on salt extrusion when ice forms (more salt = more weight).

But the fundamental mechanism of sea ice formation (which you seem to have forgotten here) is that sea water is densest at freezing point, which means that before any ice has time to form, the surface water starts sinking and mixing downwards, and the underlying warmer waters start to move up.

This is presumably what is happening in all the open areas of the arctic right now. Very cold air is blowing in from the south (from Siberia) and from the ice itself, but the air heats up very rapidly over the open ocean where the sea surface temperatures are above freezing.

The first image below shows status this morning from Nullschool, but it's essentially unchanged over the last week or so. The two blue arrows show where cold winds are blowing in over open ocean. The red figures show air temperatures at surface (in Centigrades), and the one in the middle has sea surface temperatures in paranthesis.

The thing to notice is that the air warms very considerably when blowing in over the (much warmer) ocean and that the surface of the ocean is hovering just over the freezing poing of c.a. -1.8C. As I said, this situation has been unchanged this week every time I've checked.

The second image is a very crude attempt at describing the movement of air and water at the interface. Cold air flows in over the warmer ocean, causing the air to get warmer and start to rise, allowing other cold air to sink towards the surface. The wind is carrying this turbulence forward all the time.

At the same time, the relatively static ocean waters cool at the surface and start sinking, allowing warmer deeper waters to rise.

This will continue until there is not enough heat within easy reach to keep the near-freezing waters from sinking before they freeze. This can happen because the ocean has run out of heat, or when the air is cold enough to override the sinking process (at the anecdotal -11C).

The wind is very important here, it keeps carrying the heat away from the surface, and will of couse also increase the water turbulance through wave action.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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oren

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Re: "Stupid" Questions :o
« Reply #2710 on: October 25, 2019, 04:20:04 PM »
I'm looking for recent methane concentration data from the Tiksi weather station, but the most recent data I can find on the NOAA website is over a year old.

Is the station still operational? Is NOAA still collecting this data? Or am I just being impatient?
Welcome to the forum Alumril. (Sorry I can't answer your question).

RoxTheGeologist

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Re: "Stupid" Questions :o
« Reply #2711 on: October 25, 2019, 06:35:24 PM »

...
But the fundamental mechanism of sea ice formation (which you seem to have forgotten here) is that sea water is densest at freezing point, which means that before any ice has time to form, the surface water starts sinking and mixing downwards, and the underlying warmer waters start to move up.

This is presumably what is happening in all the open areas of the arctic right now. Very cold air is blowing in from the south (from Siberia) and from the ice itself, but the air heats up very rapidly over the open ocean where the sea surface temperatures are above freezing.
..


Isn't the mixed layer in summer salinity stratified? Salinity has a much greater impact on density than temperature. I thought that the freshwater lens from melting ice effectively prevented any convection, maybe if the water to 10m (?) has been warmed and homogenized it will turn over as the surface cools.

Sadly we don't have enough buoy data to really get a good picture of what is happening to seas like the Chukchi, distant from rivers, and with much longer exposure to wave and current action because of the early ice loss. It might be that as the sea becomes ice free for longer, the ocean becomes homogenized to deeper levels, evaporation concentrates salt in the surface, sea ice takes longer to form and is thinner and works as a positive feedback year on year.

And no, I didn't suddenly forget the properties of salt water :) If it were freshwater, the warming and melting in the spring would cause the water column to turn over (like a temperate lake).


 

binntho

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Re: "Stupid" Questions :o
« Reply #2712 on: October 26, 2019, 06:06:46 AM »
Isn't the mixed layer in summer salinity stratified? Salinity has a much greater impact on density than temperature. I thought that the freshwater lens from melting ice effectively prevented any convection, maybe if the water to 10m (?) has been warmed and homogenized it will turn over as the surface cools.
I'm pretty sure the mechanism I described does not reach much further than 10m if at that. I'm talking about the very top of the ocean. And any stretch of ocean that has been ice free for months will of course have a "normal" ocean surface, the freshwater from the previous melt having long since been mixed back.

Don't forget that the ocean is vastly more voluminous than the thin skin of ice that forms on top. It's heat content is vastly bigger than the overlying air column. And last but not least, as soon as ice does start to form, the phase change releases significant amounts of heat.

Quote
And no, I didn't suddenly forget the properties of salt water :) If it were freshwater, the warming and melting in the spring would cause the water column to turn over (like a temperate lake).

Well you did seem to forget the one pertinent fact since you didn't mention it in your attemt at a theory for how heat transfer can happen in the top layers of ocean at the onset of the freezing season. Which is what this is all about.

And to be absolutely clear: My explanation above is not a private pet theory, but what has been repeatedly explained to us footlings in this forum by wiser and more knowledgeable members over the years. A very similar discussion to this one took place almost exactly a year ago, here is what I wrote at the time:

It seems that the "-11" or "-10" degrees needed before sea ice forms discussion is doomed to repeat it self regularly. As we apparently all know by now, this is not based on scientific fact but on the close observations of a single individual who seems to know what he was doing.

Those of us who have direct experience of cold climates are aware that sea-ice does not usually form in mildly frosty weather. Around the coast of Iceland sea-ice never forms, except in very rare cases in sheltered harbours, but then again winter temperatures along the coastline very rarely fall below -5 degrees C.

In Denmark, sea-ice does form every few years during prolonged cold spells where temperatures over land fall well below -10 degrees for several days running. Sea-ice starts to grow in harbours and sheltered inlets along the east coast, where there is little to no wave action, but never along the more exposed west coast.

So my pesonal experience of cold-but-not-arctic environments tells me that air temperatures of e.g. -5 are not enough to start sea ice formation in open water. But I must admit that I have no idea whether -5 is enough to start ice growing between ice floes.

Once again a vista of ignorance opens up, begging for the intrepid explorer to chart and measure.
because a thing is eloquently expressed it should not be taken to be as necessarily true
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kassy

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Re: "Stupid" Questions :o
« Reply #2713 on: October 28, 2019, 02:17:17 PM »
2016 features rather prominently on the extent graphics.

Why was that year so bad for extent? What is the short story of 2016?

And related: if i were to read back the 2016 melt thread or ASIB posts is there a good month to start?

I know this sounds like a weird question but 2015 and 2016 were really bad years for me so somehow the info ended up buried.   
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Niall Dollard

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Re: "Stupid" Questions :o
« Reply #2714 on: October 28, 2019, 03:49:52 PM »
2016 features rather prominently on the extent graphics.

Why was that year so bad for extent? What is the short story of 2016?


Short story from Nevens blog.

kassy

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Re: "Stupid" Questions :o
« Reply #2715 on: October 29, 2019, 01:49:41 PM »
Yes, the October blog post + melting season in images was enough.
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PragmaticAntithesis

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Re: "Stupid" Questions :o
« Reply #2716 on: October 30, 2019, 04:48:25 PM »
I've been looking at the extent, area and volume graphs and, over the last week, extent has rose very rapidly. However, area is rising at a much slower pace relative to other years (but still enough to overtake 2016), and volume is still the lowest in the satellite record by a large margin.

Why are the three metrics showing wildly different results despite the fact they're measuring roughly the same thing (how much ice is in the arctic)?

Tom_Mazanec

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Re: "Stupid" Questions :o
« Reply #2717 on: November 01, 2019, 12:50:20 AM »
Well, for one thing, all the MYI is gone now.
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kassy

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Re: "Stupid" Questions :o
« Reply #2718 on: November 01, 2019, 10:23:05 AM »
Area and extent are different measures and give scientists slightly different information. Some organizations, including Cryosphere Today, report ice area; NSIDC primarily reports ice extent. Extent is always a larger number than area, and there are pros and cons associated with each method.

A simplified way to think of extent versus area is to imagine a slice of swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger. A more precise explanation of extent versus area gets more complicated.

and more on:
http://nsidc.org/arcticseaicenews/faq/#area_extent
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Klondike Kat

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Re: "Stupid" Questions :o
« Reply #2719 on: November 01, 2019, 02:31:10 PM »
Yes Kassy.  Additionally, extent and area show the largest divergence during the late summer and early autumn months, as larger ocean surfaces show enough ice to be considered ice-covered in the extent measurements, but are not fully ice covered for the area measurements.  Slush qualifies as ice-covered for extent measurements, but only partially in the area measurements.  During late winter, extent and area measurements converge as most of the surface is ice-covered.  NSIDC prefers using extent as the measurements have been more consistent over time (area measurements tend to fluctate more due to thin ice and melt ponds).

Volume is calculated using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS).  The model incorporates sea ice thickness, calculated using the HYCOM-CICE model developed by DMI and sea ice concentration (different from extent or area).  Consequently, volume can differ significantly from either area or extent. 

PragmaticAntithesis

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Re: "Stupid" Questions :o
« Reply #2720 on: November 01, 2019, 08:38:28 PM »
Area and extent are different measures and give scientists slightly different information. Some organizations, including Cryosphere Today, report ice area; NSIDC primarily reports ice extent. Extent is always a larger number than area, and there are pros and cons associated with each method.

A simplified way to think of extent versus area is to imagine a slice of swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger. A more precise explanation of extent versus area gets more complicated.

and more on:
http://nsidc.org/arcticseaicenews/faq/#area_extent

Area and extent are different measures and give scientists slightly different information. Some organizations, including Cryosphere Today, report ice area; NSIDC primarily reports ice extent. Extent is always a larger number than area, and there are pros and cons associated with each method.

A simplified way to think of extent versus area is to imagine a slice of swiss cheese. Extent would be a measure of the edges of the slice of cheese and all of the space inside it. Area would be the measure of where there is cheese only, not including the holes. That is why if you compare extent and area in the same time period, extent is always bigger. A more precise explanation of extent versus area gets more complicated.

and more on:
http://nsidc.org/arcticseaicenews/faq/#area_extent

Thanks for the answers!

oren

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Re: "Stupid" Questions :o
« Reply #2721 on: November 07, 2019, 10:56:34 AM »
A small but important correction, PIOMAS does not use the Hycom-CICE model.

PragmaticAntithesis

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Re: "Stupid" Questions :o
« Reply #2722 on: November 07, 2019, 03:29:22 PM »
A small but important correction, PIOMAS does not use the Hycom-CICE model.

That leaves the obvious question: What does is use?

kassy

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Re: "Stupid" Questions :o
« Reply #2723 on: November 09, 2019, 04:23:41 PM »
Model and Assimilation Procedure
PIOMAS is a numerical model with components for sea ice and ocean and the capacity for assimilating some kinds of observations. For the ice volume simulations shown here, sea ice concentration information from the NSIDC near-real time product are assimilated into the model to improve ice thickness estimates and SST data from the NCEP/NCAR Reanalysis are assimilated in the ice-free areas.  NCEP/NCAR reanalysis SST data are based on the global daily high-resolution Reynolds SST analyses using satellite and in situ observations (Reynolds and Marsico, 1993; Reynolds et al., 2007). Atmospheric information to drive the model, specifically wind, surface air temperature, and cloud cover to compute solar and long wave radiation are specified from the NCEP/NCAR reanalysis. The pan-Arctic ocean model is forced with input from a global ocean model at its open boundaries located at 45 degrees North.

http://psc.apl.uw.edu/research/projects/arctic-sea-ice-volume-anomaly/
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oren

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Re: "Stupid" Questions :o
« Reply #2724 on: November 09, 2019, 05:54:31 PM »
Thank you Kassy. I was in a rush so gave no details.

Here's some additional information:
Quote
Model

A Pan-Arctic Ice-Ocean Modeling and Assimilation System (PIOMAS) is used for this project. PIOMAS is a coupled Parallel Ocean and sea Ice Model (POIM, Zhang and Rothrock 2003) with capabilities of assimilating ice concentration and velocity data. It is formulated in a generalized orthogonal curvilinear coordinate (GOCC) system and designed to run on computers with a single processor or massively parallel processors. PIOMAS couples the Parallel Ocean Program (POP) with a thickness and enthalpy distribution (TED) sea-ice model. The POP model is developed at the Los Alamos National Laboratory. 

The TED sea-ice model is a dynamic thermodynamic model that also explicitly simulates sea-ice ridging. The model originates from the Thorndike et al. (1975) thickness distribution theory and is recently enriched by enthalpy distribution theory (Zhang and Rothrock, 2001). It has 12 categories each for ice thickness, ice enthalpy, and snow ((Zhang et al., 2000). This multicategory TED model consists of seven main components: a viscous-plastic ice rheology that determines the relationship between ice internal stress and ice deformation (Hibler 1979), a mechanical redistribution function that determines ice ridging (Thorndike et al. 1975; Rothrock, 1975; Hibler, 1980), a momentum equation that determines ice motion, a heat equation that determines ice growth/decay and ice temperature, an ice thickness distribution equation that conserves ice mass (Thorndike et al. 1975; Hibler, 1980), an ice enthalpy distribution equation that conserves ice thermal energy (Zhang and Rothrock, 2001), and a snow thickness distribution equation that conserves snow mass (Flato and Hibler, 1995). The ice momentum equation is solved using Zhang and Hibler's (1997) ice dynamics model that employs a line successive relaxation technique with a tridiagonal matrix solver, which has been found to be particularly useful for parallel computing (Zhang and Rothrock, 2003). The heat equation is solved over each ice thickness category using a modified three-layer thermodynamic model (Winton, 2000). The configuration of the finite-difference grid of PIOMAS is shown below. 



The model grid is a stretched GOCC grid with the northern grid pole displaced into Greenland. This causes the model to have its highest resolution in the Greenland Sea, Baffin Bay, and the eastern Canadian Archipelago. This lets the model have a reasonably good connection between the Arctic Ocean and the Atlantic Ocean via the Greenland-Iceland-Norwegian (GIN) Sea and the Labrador Sea. The mean horizontal resolution is 22 km for the Arctic, Barents, and GIN (Greenland-Iceland-Norwegian) seas, and Baffin Bay. The model is one-way nested to a global POIM (GIOMAS) by imposing open boundary conditions along the southern boundaries (~ 43oN). Monthly output from GIOMAS is used for the open boundary conditions. The model was driven by the NCEP/NCAR reanalysis data. 

http://psc.apl.washington.edu/zhang/IDAO/model.html

Tom_Mazanec

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Re: "Stupid" Questions :o
« Reply #2725 on: November 11, 2019, 07:16:20 PM »
Why do they call it the Antarctic Peninsula, instead of the Palmer Peninsula like when I was in school?
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blumenkraft

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Re: "Stupid" Questions :o
« Reply #2726 on: November 11, 2019, 07:20:10 PM »
Quote
The Antarctic Peninsula, known as O'Higgins Land in Chile, Tierra de San Martin in Argentina, and originally known as the Palmer Peninsula in the US and as Graham Land in Great Britain, is the northernmost part of the mainland of Antarctica, located at the base of the Southern Hemisphere.

Looks like they told you an American centric worldview in school.

Who would have thought so? ;)
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Re: "Stupid" Questions :o
« Reply #2727 on: November 11, 2019, 09:40:56 PM »
I vote O'Higgin's Land .. home of the wayward Irishman .. :) b.c.
2007 + 5 = 2012 + 4 = 2016 + 3 = 2019 ...